#include <fstream>
#include <vector>
#include <algorithm>
#include <queue>
#include <cstring>

using namespace std;

ifstream fin("pscnv.in");
ofstream fout("pscnv.out");

const int INF = 0x3f3f3f3f;

int N, M, x, y;
int D[250005];
vector<pair<int, int> > V[250005];
queue<pair<int, int> > Q;

void bellman(int nod)
{
    memset(D, INF, sizeof(D));
    D[nod] = 0;
    Q.push(make_pair(nod, 0));

    while (!Q.empty())
    {
        int now = Q.front().first;
        int nowk = Q.front().second;
        Q.pop();

        for (vector<pair<int, int> >::iterator it = V[now].begin(); it != V[now].end(); ++it)
        {
            int k = max(nowk, it->second);
            if (k < D[it->first])
            {
                D[it->first] = k;
                Q.push(make_pair(it->first, k));
            }
        }
    }
}

int main()
{
    fin >> N >> M >> x >> y;
    for (int i = 1, nod1, nod2, k; i <= M; ++i)
    {
        fin >> nod1 >> nod2 >> k;
        if (nod1 == nod2)
            continue;
        V[nod1].push_back(make_pair(nod2, k));
    }

    bellman(x);

    fout << D[y] << '\n';

    fin.close();
    fout.close();
    return 0;
}